This invention relates generally to hatch covers for railway hopper cars, and more particularly to a hatch cover constituted by a structural sandwich laminate in which a balsa wood core panel is interposed between fiberglass facing skins.
The conventional railway hopper car is loaded through a roof hatch which is centered on the roof and straddled by narrow walkways, the hatch being closed by hinged hatch covers. The typical hopper car has one continuous hatch extending almost the full length of the roof and a set of hinged hatch covers fabricated of steel and arranged in tandem, each cover closing a respective portion of the hatch.
Steel hatch covers are heavy and cumbersome, and in order to provide covers which can be manually raised and lowered without difficulty, each steel cover must be relatively short to provide a workable weight. Hence several steel covers are normally required to close the entire roof hatch of a hopper car.
In recent years, efforts have been made to replace steel hatch covers with light-weight covers molded of fiberglass-reinforced plastic material. A molded plastic hatch cover has many advantages over steel; for it is corrosion-resistant and much lighter in weight; it is easier to move between its opened and closed positions so that fewer covers of an appropriate length may be used to close a hopper car hatch. Moreover, by using reinforced fiberglass hatch covers, one thereby substantially reduces the overall unloaded weight of the hopper car.
Where the molded fiberglass reinforced plastic hatch cover is of one-piece construction, as disclosed, for example, in the Zeller U.S. Pat. No. 3,796,168, it then possesses an inherent flexibility. This makes it difficult to maintain a weather-tight seal between the cover and hatch unless one provides many closely-spaced clamps located about the entire periphery of the cover. As noted in the Zeller patent, since these plastic covers range in size up to 14 feet in length, while being only 21/2 feet wide, the necessity for so many clamps renders such plastic covers impractical, not only because of the cost entailed by a large number of clamps, but also due to the working time required to lock and release the clamps.
Moreover, should one of the clamps be left unclamped--a not uncommon occurrence--dirt, rain and water are then free to enter the hopper car interior and may ruin the cargo stored therein. Zeller seeks to solve this problem by adding weather stripping to his one-piece fiberglass reinforced plastic panel, but this solution does not overcome other drawbacks of a hatch cover of this type arising from its inherent flexibility and structural weakness.
The Ingram U.S. Pat. No. 3,605,639 points out that fiberglass plastic hatch covers of the type then known not only lack the rigidity of metal covers, but that they are prone to cracking when thrown open to one side against a roof walkway. To overcome these problems, Ingram provides a fiberglass hatch cover of hollow construction, the light-weight cover being reinforced by internal fiberglass trusses to impart rigidity and improved load-bearing strength thereto. While trussed covers of the Ingram type have obvious advantages over single-piece plastic covers, their construction entails a relatively complex and costly manufacturing procedure.